Crystal Defenders is a tower defense video game by Square Enix. The game was originally released under the title Crystal Guardians (クリスタル ガーディアンズ Kurisutaru Gādianzu) for mobile phones. Versions for the iOS, WiiWare, Xbox Live Arcade, and PlayStation Network were later released under its current title.

Crystal Defenders takes place after the events of Final Fantasy Tactics A2: Grimoire of the Rift and features units from the Final Fantasy Tactics series. The objective of the game is for the player to stop waves of monsters from stealing a cache of crystals in a maze by strategically positioning units to destroy them before they escape with their loot. Each unit has their own special attributes, and have particular strengths and weakness against certain enemies.

The game features 300 stages (waves of monsters) spread across three chapters of increasing challenge.